SPP1 and Spondyloenchondrodysplasia with immune dysregulation: Subsequently, based on earlier work in mouse (12), it was suggested that the immunological features of SPENCD might relate to a failure of mutant TRAP to dephosphorylate osteopontin (OPN) in plasmacytoid dendritic cells (pDCs), leading to persistent Toll-like receptor 9 (TLR9) signalling (13).